I used to use a small freeware program called "Bounce Spam Mail". What is does is send a fake "bounce" message that the user is unknown. But I now have a pay account with SpamCop. I use TheBat! as my mail client and in there I have a script (filter) that with a key stroke I can submit and report spam to them and then THEY send the spam reports to the ISP for the spammer. Since having done this, I very rarely get spam in my INBOX.